This project is designed to investigate the role of the sympathetic nervous system (SNS) in canine gastric secretion. For each experiment, three types of data will be collected: 1) basal and pentagastrin stimulated gastric secretion rates, 2) serum and gastric tissue levels of catecholamines, 3) changes in the ultrastructure of the gastric mucosa and submucosa by electron-microscopy. (Phase I) The effects of 6-hydroxydopamine (6-OHDA) on these three parameters will be measured in three adult dogs fitted with gastric cannulas, after control measurements and biopsy. (Phase II) Twelve dogs are divided into four groups and receive base line testing as above. Group I dogs have a surgical sympathectomy and repeat testing followed by treatment with 6-OHDA. Group II dogs receive treatment with 6-OHDA first, followed by surgical sympathectomy. Group III dogs have Heidenhain pouches in addition to gastric fistulas. After base line testing, they will receive surgical sympathectomy followed by 6-OHDA. Group IV dogs will undergo adrenalectomy followed by surgical sympathectomy. The results are expected to outline the effect and usefulness of 6-OHDA as a model of chemical sympathectomy in the study of gastric secretion. A comparison of the influence of the circulating amines versus locally released amines from adrenergic nerve endings on three parameters listed above should be possible. Also the effect of vagotomy on the surgical and chemical sympathectomized dogs will be studied. Finally the data should establish whether the SNS has an inhibitory influence on gastric secretion. Conclusions will be supported by measurements of tissue catecholamines and morphologic changes at the ultrastructural level of the gastric.